Charge Air Pressure System, Checking

Charge air pressure system, checking
Charge air pressure regulation, checking
Special tools, workshop equipment, testers, measuring instruments and auxiliary items required





^ V.A.G 1551 scan tool

Note: The vehicle system tester V.A.G 1552 can be used instead of the VAG 1551 scan tool, however a print-out is not possible.





^ V.A.G 1551/3 Cable
Check conditions
^ No faults must be stored in DTC memory.
^ No leaks on intake and exhaust systems.
^ Engine oil temperature min. 80°C

Test sequence
- The charge air pressure is measured under full load, whilst driving or on a rolling road.
Observe applicable safety precautions when carrying out a road test.
- Connect VAG 1551 scan tool ((V.A.G 1552). Start engine and select engine electronics control module with "Address word" 01. Connecting scan tool and selecting engine control module.





Indicated on display:
- -Press keys O and 8 for the function "Read measured value block" and confirm entry with Q key.





Indicated on display:
- Press keys 1, 1 and 4 for "Display group number 114" and confirm entry with Q key.





Indicated on display: (1 to 4 = Display zones)
- Check duty cycle of wastegate bypass regulator valve (N75) in display zone 4 (at full throttle between 1800 to 2300 RPM) during a test drive or on a rolling road. Specification: 5.0 to 95.0 %

If the specification is obtained:
- Change to display group 115 as follows: V.A.G 1551: Press key 3 V.A.G 1552: Press key ^





Indicated on display: (1 to 4 =Display zones)
- Check charge air pressure (actual value) at full throttle in display zone 4:

On rolling road
In 3rd gear or in 2nd driving range

During test drive
Vehicles with manual transmission
- Accelerate in 2nd gear with full throttle.

Vehicles with automatic transmission.
- Manually select drive mode 4 (Tiptronic) and accelerate vehicle from a low speed at Wide Open Throttle (WOT, without Kick-Down, transmission no longer shifts down).

Engine speed AWD, AWW
- Press the print button between 1800 to 2300 RPM and read the charge air pressure actual value in display zone 4. Specification: 1350 to 1750 bar

Engine speed AWP
- Press the print button between 1800 to 2300 RPM and read the charge air pressure actual value in display zone 4. Specification: 1700 to 2000 bar

Continued for all vehicles
- Compare actual charge air pressure value with specified charge air pressure value in display zone 3 Difference: max. 100 mbar

Note: Repeat the measurement if the charge air pressure has not fully built-up or there is a large difference between specified and actual values.

- Press the (arrow) key.
- Press keys O and 6 for the "End output" function and confirm input with the Q key.
- Switch off ignition.

If the charge air pressure is exceeded:
- Check charge air pressure sensor (G31).
- Test wastegate bypass regulator valve (N75). (Hose from turbocharger via valve to pressure unit not blocked when connector is pulled off).
- Check pressure unit for charge air pressure regulating valve is securely mounted on turbocharger.
- Check pressure unit
- Check shaft mount for charge air pressure regulating valve in turbocharger for ease of movement. When corroded together, replace turbocharger.
If the the charge air pressure is not attained:
- Check charge air pressure sensor (G31).
- Check Wastegate bypass regulator valve (N75).
- Check shaft mount for charge air pressure regulating valve in turbocharger for ease of movement. When corroded together, replace turbocharger.
- Turbocharger malfunctioning. Replace turbocharger.
- Check DTC memory.
- Read out readiness code.
- If the DTC memory has been erased or the engine control module separated from the permanent positive, the readiness code must be generated again.